6. High-yield investment opportunities

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A high-yield investment program (HYIP) is essentially just a Ponzi scheme, a principle with which everyone and his grandma is familiar with by now — investors are promised an absurdly high return, and initially they get it (or rather, they get the money of the new investors who were promised the same thing). The scheme is completely unsustainable after a few levels, which is why the people who implement them rely on early investors to spread news of their success.

HYIPs are thoroughly illegal, and the simple rule of thumb is that any promised high return that seems too good to be true almost certainly is.